Ram Air Turbine (RAT) systems are used in contemporary aircraft as emergency or supplemental power systems. They typically have a turbine, with a rotating hub and a plurality of blades, operably coupled to a generator to provide the driving source for the generator. Initially in flight they are stowed in a compartment of the aircraft fuselage, covered by a compartment door. When needed as a source of emergency or supplemental power, the RAT system is deployed from the fuselage into the surrounding airstream, which drives the blades to rotate the generator to extract energy from the airstream.
As power requirements for aircraft systems increase, the power generation capabilities of RAT systems continue to increase. Higher power generators tend to be configured to rotate at speeds greater than the rotational speed of the turbine by utilizing a gearbox between the turbine and the generator. The higher power generators, including the gearbox, tend to generate sufficient heat to make it impossible to cool solely by the airstream and use liquid cooling systems, including a heat exchanger, which projects into the airstream.